Two truck drivers had to abruptly stop their truck

Realizing that the truck they were driving was too tall for the underpass of a bridge, the two truck drivers had to abruptly stop the vehicle. They looked at the bridge, trying to think of a way they could possibly drive under it.
A little boy saw the 2 drivers and said to them:
“The truck is only a few inches too tall. Why don’t you try taking some air out of the tires so you can pass under the bridge”
The men looked at the boy with perplexed expressions on their faces and said:
“Won’t work, it’s missing a few inches at the top not at the bottom”